update agent skill with YAGNI

AGENTS.md

@@ -16,13 +16,14 @@ An implementation of the RPG Combat rules engine. There are six user stories des
 
 This project combines three practices:
 
-1. **Allium** (`.allium` specs) — formal behavioural specifications that capture *what* the system does
+1. **Allium** (`.allium` specs) — formal behavioural specifications that capture _what_ the system does
 2. **fast-check** — property-based testing that verifies those properties hold across thousands of random inputs
 3. **"I can't believe it's not Haskell"** — TypeScript with ADTs, value objects, and immutability
 
 ### Step 1: Spec with Allium
 
 Use the Allium skills to formalize user stories into `.allium` specs:
+
 - `/skill:elicit` — explore requirements with stakeholders
 - `/skill:distill` — extract specs from existing code
 - `/skill:tend` — evolve specs as understanding deepens
@@ -38,13 +39,10 @@ import fc from 'fast-check';
 import { Character } from './domain';
 
 // Invariant: "A character's health is never negative"
-fc.property(
-  fc.integer({ min: 0, max: 1000 }),
-  (initialHealth) => {
-    const c = new Character({ name: 'hero', health: initialHealth });
-    return c.health >= 0;
-  }
-);
+fc.property(fc.integer({ min: 0, max: 1000 }), (initialHealth) => {
+  const c = new Character({ name: 'hero', health: initialHealth });
+  return c.health >= 0;
+});
 
 // Property: "Dealing damage reduces health, capped at 0"
 fc.property(
@@ -58,13 +56,13 @@ fc.property(
     const t = new Character({ name: target, health: 1000 });
     a.dealDamage(t, damage);
     return t.health === Math.max(0, 1000 - damage);
-  }
+  },
 );
 ```
 
 ### Step 3: "I can't believe it's not Haskell"
 
-Use TypeScript's type system to encode domain constraints:
+Use TypeScript's type system to encode domain constraints. Add only code necessary to make the property pass, no more:
 
 ```typescript
 // ADTs via discriminated unions
@@ -77,9 +75,15 @@ class Health {
     if (n < 0) throw new Error('Health cannot be negative');
     return new Health(n);
   }
-  get value() { return this.value; }
-  add(n: number) { return Health.create(this.value + n); }
-  sub(n: number) { return Health.create(Math.max(0, this.value - n)); }
+  get value() {
+    return this.value;
+  }
+  add(n: number) {
+    return Health.create(this.value + n);
+  }
+  sub(n: number) {
+    return Health.create(Math.max(0, this.value - n));
+  }
 }
 
 // Immutable entities
@@ -98,16 +102,28 @@ class Character {
 }
 ```
 
+
+
 **Key principles:**
+
 - **ADTs over classes** — use discriminated unions for state/variants
 - **Value objects over primitives** — `Health`, `Damage`, `Level` instead of `number`
 - **Immutability** — no `this.health = ...`, return new instances
 - **Invariants at boundaries** — constructors enforce invariants, not getters/setters
 - **Pure functions** — domain logic has no side effects, testable in isolation
+- **YAGNI** Write the minimum code necessary to make the current property pass. 
+
+Before writing a method, ask:
+
+ 1. Does a story property require this? If no → don't write it.
+ 2. Does this method touch a concept from a different story? If yes → it's scope creep.
+ 3. Am I implementing something because it feels useful, not because a property forces it? If yes → stop.
+
+
 
 ### Example: Damage Property
 
-From user story: *"When damage received exceeds current Health, Health becomes 0 and the character dies"*
+From user story: _"When damage received exceeds current Health, Health becomes 0 and the character dies"_
 
 ```typescript
 // Allium invariant (in .allium spec)
@@ -122,13 +138,14 @@ fc.property(
     const c = new Character({ name: 'goblin', health: Health.create(health) });
     c.takeDamage(Damage.create(damage));
     return c.health.value === Math.max(0, health - damage);
-  }
+  },
 ).check(/* ... */);
 ```
 
 ## Skill Invocation
 
 Allium skills are available in this project:
+
 - `/skill:allium` — entry point and language reference
 - `/skill:elicit` — explore requirements
 - `/skill:distill` — extract specs from code
@@ -137,4 +154,5 @@ Allium skills are available in this project:
 - `/skill:weed` — check spec-code alignment
 
 Domain workflow skill:
+
 - `/skill:user-story-conversation` — Card, Conversation, Confirmation workflow with Example Mapping, Allium specs, and fast-check properties